A portable electronic device (1) comprises a control device (201), a chemical sensor (226) that is sensitive to a chemical analyte, and an output device (230-236) coupled to the control device. The control device carries out a measurement with the chemical sensor. It determines whether the portable electronic device has been handled appropriately during the measurement. If the portable electronic device has not been handled appropriately, the control device operates the output device to present information to a user of the portable electronic device. The information may include instructions to handle the portable electronic device in a specific manner. Determination whether the portable electronic device has been handled appropriately may be based on one or more parameters measured by a second sensor (211-225) that is different from the chemical sensor (226).